Re: Retrieving the EXIF date/time from 250k images
Re: Retrieving the EXIF date/time from 250k images
- Subject: Re: Retrieving the EXIF date/time from 250k images
- From: Alex Zavatone via Cocoa-dev <email@hidden>
- Date: Tue, 16 Aug 2022 15:00:52 -0500
I love experimenting with processes like this. Create as many operation
processes as you have cores on your box and run a few tests to see how quickly
the operations complete. Try it with 2x the number of cores, 1x the number of
cores, 1/2 x the number of cores and the number of cores + 1 and the number of
cores - 1 to see if there are any substantial differences in time to completion.
But as the others have said, GCD and NSOperationQueue were made for these
things. If you’re actually trying to get work done and not researching for
your own benefit, those are the ones to use. They do all the heavy lifting for
you are are easy to implement.
Cheers.
Alex Zavatone
> On Aug 16, 2022, at 2:37 PM, Jack Brindle via Cocoa-dev
> <email@hidden> wrote:
>
> Instead of using NSOperationQueue, I would use GCD to handle the tasks.
> Create a new Concurrent queue
> (dispatch_queue_create(DISPATCH_QUEUE_CONCURRENT)), then enqueue the
> individual items to the queue for processing (dispatch_async(), using the
> queue created above). Everything can be handled in blocks, including the
> completion routines. As Christian says the problem then is that data may not
> be in the original order so you will probably want to sort the returned
> objects when done. This should significantly speed up the time to do the
> whole task.
>
> Jack
>
>
>> On Aug 16, 2022, at 12:26 PM, Steve Christensen via Cocoa-dev
>> <email@hidden> wrote:
>>
>> You mentioned creating and managing threads on your own, but that’s what
>> NSOperationQueue —and the lower-level DispatchQueue— does. It also will be
>> more efficient with thread management since it has an intimate understanding
>> of the capabilities of the processor, etc., and will work to do the “right
>> thing” on a per-device basis.
>>
>> By leveraging NSOperationQueue and then keeping each of the queue operations
>> focused on a single file then you’re not complicating the management of what
>> to do next since most of that is handled for you. Let NSManagedObjectQueue
>> do the heavy lifting (scheduling work) and focus on your part of the task
>> (performing the work).
>>
>> Steve
>>
>>> On Aug 16, 2022, at 8:41 AM, Gabriel Zachmann <email@hidden> wrote:
>>>
>>> That is a good idea. Thanks a lot!
>>>
>>> Maybe, I can turn this into more fine-grained, dynamic load balancing (or
>>> latency hiding), as follows:
>>> create a number of threads (workers);
>>> as soon as a worker is finished with their "current" image, it gets the
>>> next one (a piece of work) out of the list, processes it, and stores the
>>> iso_date in the output array (dates_and_times).
>>> Both accesses to the pointer to the currently next piece of work, and the
>>> output array would need to be made exclusive, of course.
>>>
>>> Best regards, Gabriel
>>
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